1. Field of the invention
This invention relates to the production and recording of inhomogeneities in otherwise homogeneous objects having a plane or locally substantially plane surface, by ultrasonic examination according to the pulse echo method. The production and recording of correct and well-defined images of internal inhomogeneities is a matter of the greatest importance for the correct location and sizing of internal flaws in materials and welded joints, and thus for the safety and fitness for purpose of important structures and installations.
2. Background of the Prior Art
In the ultrasonic examination art, great efforts have been made to develop improved systems for the location and sizing of flaws in materials and welded joints, in particular systems producing easily readable images of internal flaws. In many systems this has been made possible through the use of digital computing means including electronic matrix memories for the storage of echo data which may then be analysed, displayed on video monitors as grey scale or colour images, and permanently recorded by magnetic recording means or permanent prints.
Examples of extensive descriptions of ultrasonic examination systems of this kind for producing sectional views (B-scan displays) and plan views (C-scan displays) are Flathery U.S. Pat. No. 3,673,860 and Beller U.S. Pat. No. 3,857,052. Improved systems for the storage and display of complete projection images (P-scan displays) of flaws located in the interior of materials and welded joints have been described in Lund U.S. Pat. Nos. 3,939,697 and 4,226,122. However, none of the prior art examination systems have been entirely satisfactory.
The major and overriding problems in ultrasonic examination have not been associated with the ultrasonic equipment and techniques themselves, but with the complete and objective analysis and interpretation of the data, in particular the exact location and sizing of flaws. Small, but significant anomalies in the data are often overlooked, because the data is irregular and noisy, and the unavoidable beam spread of the ultrasonic sound beam leads to indistinct outlines of the flaw images.